1. Field of the Invention
The present invention relates to a method for redefining a notch filter of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads can magnetize and sense the magnetic fields of the disk to write and read data, respectively. The heads are coupled to an pivoting actuator arm that has a voice coil motor.
Data is typically stored on tracks that extend radially across the disk surfaces. The voice coil motor can be energized to pivot the actuator arm and move the heads to different track locations. Each track is typically divided into a number of sectors. Each sector contains a number of servo bits that are read to produce a position error signal (PES). The PES is processed and used to center the heads on the tracks in accordance with a servo routine.
Movement of the heads from track to track may induce a resonant movement of the actuator arm at a resonant frequency. The resonant movement will cause an oscillating movement of the heads. The oscillating movement will increase the servo time required to center the heads. To compensate for such resonant movement the disk drives typically include a notch filter that filters out a band of frequencies centered about the resonant frequency. It is desirable to periodically update the centering frequency of the notch filter and generally redefine the filter. This is sometimes done by sweeping the excitation signal of the voice coil motor and then determine which frequency produces the greatest PES response. Sweeping the excitation signal can be a time consuming procedure. It would be desirable to redefine the notch filter in a more time efficient manner.